High energy density and high energy efficiency are critical qualities for increasing success in renewable clean energy applications. Redox flow batteries (RFBs) can meet many needs by providing conversion between electrical energy and chemical energy. However, RFBs can be associated with low energy density and high cost due to the low concentration of active materials and the use of expensive catalysts and/or membranes. For example, the energy density of a traditional all-vanadium redox flow battery is in the range of approximately 20-50 Wh/L depending on the choice of electrolyte. Traditional zinc-based flow batteries, such as a Zn—Br flow battery (ZBB), demonstrate slightly higher values of energy density. However, the performance of common ZBBs are often limited by their low energy efficiency and short cycling life. Furthermore, the bromine gas is very corrosive and hazardous, leading to serious health and environmental concerns. The low energy density not only limits the application of flow battery to stationary energy storage, but also increases the form factor and cost of the flow battery. Based on the absence of RFBs with high energy density and low cost, there is a need to develop improved flow battery systems.